[kcms/users] Offer to change kwallet password when changing login password

Right now, when a user changes their login password, their KWallet password is not changed. For users whose KWallet password was the same as their login password, this causes the two passwords to get out of sync, and then the user will be prompted to unlock their wallet the next time they log in. If they use their new password, it won't work. This is very very frustrating if you don't know what's going on.

Now, when you change the login password of your own user account, and you have a wallet named "kdewallet" (the default one) in your list of wallets, you will be prompted to change the password of that wallet to match the new login password. This is optional and you don't have to do it, and you won't be prompted to do so if you don't have a wallet named "kdewallet", which indicates that you have a customized KWallet setup and you presumably know what you're doing.

The UX here was tested on my wife who encountered this situation today and was quite annoyed by it. She gave the current version her approval. :)

simplescreenrecorder-2020-10-17_22.21.07

BUG: 389030 FIXED-IN: 5.21

cc @teams/vdg